1. Field of the Invention
The invention relates to the art of driving an ink jet recording head that ejects an ink droplet from a nozzle opening by displacing a resilient plate forming a pressure chamber with a rod-like piezoelectric vibrating element and compressing the pressure chamber by such displacement.
2. Prior Art
As disclosed in Japanese Patent Publication No. Hei 2-24218, ink jet recording heads having disk-shaped piezoelectric vibrating substrates secured to a resilient plate forming pressure chambers has heretofore been used for recording apparatuses. In the ink jet recording heads of this type, displacement of each piezoelectric vibrating element is so small that a large effective area must be provided, which in turn ensures a relatively large area. These ink jet recording heads are of such a structure that the pressure chambers are located distant from the nozzle openings and communicate with the nozzle openings through flow paths. This not only makes the recording heads large in structure, but also entails the complicated operation of adjusting the fluid resistances of the respective ink flow paths so as to be consistent.
To overcome the above problems, proposed in, e.g., the specification of U.S. Pat. No. 4,697,193, is an ink jet recording head that produces ink droplets by arranging rod-like piezoelectric vibrating elements and abutting these elements against the resilient plate that forms the pressure chambers to allow the piezoelectric vibrating elements to vibrate vertically. Since the piezoelectric vibrating elements can be disposed so as to confront the nozzle openings in this type of ink jet recording head, the flow paths for connecting the pressure chambers to the nozzle openings can be dispensed with. In addition, the piezoelectric vibrating elements can be prepared in lamination form, which contributes not only to decreasing the drive voltage, but also to improving the print speed owing to the fact that the eigenfrequency of the piezoelectric vibrating element is comparatively large and that this permits high-speed driving of the head.
The ink jet recording head utilizing vertical vibration is driven by a so-called "pull-and-strike" method, in which a drive voltage is applied to the piezoelectric vibrating elements to contract them before forming dots and the drive voltage is then discharged to expand the piezoelectric vibrating elements so that ink droplets are produced.
Such pull-and-strike method not only allows elastic energy prestored in the piezoelectric vibrating elements and the vibrating plate to be utilized, but also ensures that ink will be introduced to the pressure chambers. On the other hand, if the frequency of repeating the operation of the piezoelectric vibrating elements is increased to improve the print speed, the meniscus varies from one position to another each time an ink droplet is formed, thus varying the size and speed of the ink droplets and making the print quality inconsistent.
To avoid these problems, a driving technique in which the piezoelectric vibrating element contracting speed is set to a smallest possible value so as to minimize the varying distance of the meniscus; the piezoelectric vibrating elements are held as contracted for a predetermined time period until the meniscus returns to the original position and stays stationary; and the piezoelectric vibrating elements are expanded by applying a second drive voltage.
This drive technique contributes to ensuring a stable print quality, but imposes a new problem that the high-speed response of each piezoelectric vibrating element cannot be fully utilized.